The present invention relates to a device for detecting gas density for use in an internal combustion engine, and, more particularly, to a gas density detecting device for converting the quantity of air drawn into an engine into a mass flow value.
In automobile engines, when running at high altitudes or under hot climatic conditions, the air density becomes rarefied, so that an air consumption ratio of a fuel mixture is relatively dense as compared with that of the fuel mixture when running at low altitude or under cold climatic conditions and thus a exhaust performance and a fuel consumption efficiency are decreased. The air consumption ratio is therefore usually corrected in accordance with a change in air density, but particularly in the case of an engine equipped with an electronically controlled fuel injecting device, the change of such air density is detected and converted into an electric signal and the electric signal is supplied to a fuel control circuit as a correction signal to adjust the quantity of injected fuel.
A device for detecting air density has been variously proposed as disclosed in Japanese Utility Model Laid-Open No. 4,880/79, for example, the density is often detected by the use of a bellows in which a predetermined gas is sealed based on Boyle-Charles' Law.
This device is comparatively inexpensive, but if the bellows portion is subject to chafing, a measurement error can be generated, and the possibility of a variation in device characteristics at the time of production is comparatively large, so that the use of this type of device is limited.
Moreover, gas density detection is easily influenced by external factors other than a gas according to the measuring condition of the gas to be measured, so that it is difficult to precisely detect gas density.